1. Field of the Invention
The present invention relates to radio frequency amplifiers preferably used in satellite communication transmitters and transceivers.
2. Description of the Related Art
A radio frequency amplifier used in a millimeter-wave band (which has a frequency range from 20 to 40 GHz) is illustrated in FIGS. 6 and 7. A casing 31 made of metal, such as brass serves as a heat sink. The casing 31 includes a storage part 31a having an opening at an upper part and a side wall 31b (see FIG. 6) that surrounds the storage part 31a. 
A circuit board 32, which is a printed circuit board, includes a pair of holes 32a and 32b shown in FIG. 6. As shown in FIG. 7, wiring patterns 33a and 33b, which are conductive, are positioned on a top surface of the circuit board 32. A filter 34, which is made of oblique conductive patterns, is positioned between the wiring patterns 33a and 33b between the holes 32a and 32b. 
The filter 34 separates the top surface of the circuit board 32 into first and second regions R1 and R2 (see FIG. 7). As shown in FIG. 6, a ground pattern is positioned on the back surface of the circuit board 32. The ground pattern is disposed on a bottom portion 31c of the storage part 31a and the circuit board 32 is mounted in the storage part 31a by appropriate means.
Field effect transistors (FETs) 35a and 35b are inserted into the holes 32a and 32b of the circuit board 32. The FETs 35a and 35b are fixed through the holes to the bottom portion 31c of the casing 31 using electrically conductive adhesive. Wires 36 are bonded to the FETs 35a and 35b, and hence, the FETs 35a and 35b are connected to the wiring patterns 33a and 33b, which are formed in the first and second regions R1 and R2, respectively.
Various electrical components are soldered to the wiring patterns 33a and 33b formed in the first and second regions R1 and R2, respectively. With these electrical components and the FETs 35a and 35b, a first amplifier circuit 37a that includes a bias circuit is assembled in the first region R1, and a second amplifier circuit 37b that includes a bias circuit is assembled in the second region R2. A metal cover is mounted by appropriate means to cover the opening of the casing 31 to shield the storage part 31a. 
In this conventional radio frequency amplifier, the filter 34 is formed of oblique conductive patterns. These conductive patterns can cause large transmission losses and can create distortion in the amplifier circuits 37a and 37b. Thus, the performance of this radio frequency amplifier is not always efficient and isolation between the first and second amplifier circuits 37a and 37b can be compromised.
A radio frequency amplifier includes a casing, preferably made of metal, which includes a storage part. A circuit board is positioned within the storage part, on which first and second amplifier circuits are positioned. A filter is positioned between the first and second amplifier circuits. The filter includes a waveguide filter that is preferably configured to attenuate or dampen interfering electrical signals, such as noise or electromagnetic interference that can adversely affect the first and second amplifier. The waveguide filter is positioned within the storage part between the first and second amplifier circuits and preferably provides electrical shielding between the first and second amplifier circuits.
The first and second amplifier circuits preferably include first and second amplifying elements, respectively, and the amplifying elements may be non-packaged or bare chips. The first and second amplifying elements can be connected to a wiring pattern on the circuit board, with the waveguide filter positioned between the amplifying elements.
The waveguide filter preferably includes a main body preferably formed of metal and having a cavity. The main body preferably separates the storage part into first and second chambers. The first amplifier circuit is preferably formed within the first chamber. The second amplifier circuit is preferably formed within the second chamber.
The cavity of the main body is preferably a concave cavity that that opens from the underside of the main body. The opening is preferably positioned above a bottom portion of the casing, wherein the bottom portion and the main body comprise the waveguide filter.
The bottom portion of the casing preferably includes a cavity that is also preferably a concave cavity. The cavity of the casing and the cavity of the main body is preferably arranged such that the cavities substantially align with each other, with a circuit board positioned between the bottom portion and the main body. A probe, preferably comprised of a portion of the wiring pattern of the circuit board, is preferably located in the storage part. The radio frequency amplifier may further include a cover that conceals the opening of the storage part. An interior surface of the cover preferably contacts a top surface of the waveguide filter.
According to a preferred embodiment, the transmission loss and distortion of amplifier circuits are relatively small in comparison to some conventional circuits, which provide a high-performance radio frequency amplifier. Unlike some conventional circuits, the first and second amplifier circuits are not directly coupled, and hence, electrical isolation is improved. Moreover, the structure of a radio frequency amplifier is simplified, and the radio frequency amplifier can be fabricated at a low cost. Furthermore, reliable electrical shielding between the first and second amplifier circuits is provided by a main body, further improving electrical isolation. Since a casing can preferably comprise a part of the waveguide filter, the structure of the waveguide filter is simplified. The waveguide filter preferably has a reduced height which reduces the cost of the waveguide filter. A circuit board can be easily mounted, and probes are preferably comprised of wiring patterns.